1. Field of the Invention
The present invention generally relates to position prediction devices and methods. The present invention particularly relates to a device and a method for predicting shaft rotational positions with the predictions being utilized to control a magnitude and a duration of current being applied to stator windings of a motor.
2. Description of the Related Art
A prior art motor shaft position prediction technique involves a course-resolution position sensor 16, a course-resolution position sensor 17, and a course-resolution position sensor 18 disposed in an equidistant of 60 degrees about a motor shaft 10 and a rotor 11 attached thereto as shown in FIGS. 1A-1D. Referring to FIGS. 1A-1D, a magnet 12 displaying a north surface N, a magnet 13 displaying a south surface S, a magnet 14 displaying a north surface N, and a magnet 15 displaying a south surface S are attached to rotor 11.
Each magnet 12-15 extends a radial distance of 90 degrees whereby collectively magnets 12-15 extend over a 360-degree radius of rotor 11. FIG. 1A illustrates shaft 10 and rotor 11 at a 0 degree or 360 degree position. FIG. 1B illustrates shaft 10 and rotor 11 at a 90 degree position whereby magnets 12-15 have been rotated 90 degrees in a clockwise direction as indicated by arrow A. FIG. 1C illustrates shaft 10 and rotor 11 at a 180 degree position whereby magnets 12-15 have been rotated an additional 90 degrees in a clockwise direction as indicated by arrow A. FIG. 1D illustrates shaft 10 and rotor 11 at a 270 degree position whereby magnets 12-15 have been rotated an additional 90 degrees in a clockwise direction as indicated by arrow A.
Sensor 16 provides a rotational positional signal RPS1 at a logic high level LH whenever sensor 16 is predominately facing magnet 12 or magnet 14, and provides rotational positional signal RPS1 at a logic low level LL whenever sensor 16 is predominately facing magnet 13 or magnet 15.
Sensor 17 provides a rotational positional signal RPS2 at a logic high level LH whenever sensor 17 is predominately facing magnet 12 or magnet 14, and provides rotational positional signal RPS2 at a logic low level LL whenever sensor 17 is predominately facing magnet 13 or magnet 15.
Sensor 18 provides a rotational positional signal RPS3 at a logic high level LH whenever sensor 18 is predominately facing magnet 12 or magnet 14, and provides rotational positional signal RPS3 at a logic low level LL whenever sensor 18 is predominately facing magnet 13 or magnet 15.
The following TABLE 1 illustrates the logic levels of rotational position signals RPS1-S3 for each incremental rotational position of shaft 10 and rotor 11:
From TABLE 1, it is understood that, for every 30 degrees incremental position of motor shaft 10 and rotor 11, only one of the rotational position signals RPS1-S3 transitions from one of the logic levels to the other logic level. As such, a logic unit (not shown) is utilized to provide a rotational positional signal RPS4 as a function of each logic level transition of rotational positional signals RPS1-S3, whereby, as known in the art, rotational positional signal RPS4 is an indication of each 30-degree incremental rotation position of motor shaft 10 and rotor 11 as illustrated in FIG. 2.
A graph illustrating time stamps t0-12 of each transition of rotational positional signal RPS4 over the 360 degree rotation of motor shaft 10 and rotor 11 with motor shaft 10 and rotor 11 experiencing a constant rotational speed as known in the art is shown in FIG. 3A. Referring to FIG. 3A, each 30-degree incremental rotation of motor shaft 10 and rotor 11 occurs every time interval ti1.
A graph illustrating a prediction, as known in the art, of each position of motor shaft 10 and rotor 11 over the 360 degree rotation of motor shaft 10 and rotor 11 with motor shaft 10 and rotor 11 experiencing a constant rotational speed during time stamps t0-12 is shown in FIG. 3B. Referring additionally to FIG. 3B, the prediction of each position is based on a constant slope equal to 30 degrees divided by time interval ti1.
A graph illustrating time stamps t1-12 of each transition of rotational positional signal RPS4 over the 360 degree rotation of motor shaft 10 and rotor 11 with motor shaft 10 and rotor 11 experiencing an increase in rotational speed between time stamp t6 and time stamp t7 as known in the art is shown in FIG. 4A. Referring to FIG. 4A, each 30 degree incremental rotation of motor shaft 10 and rotor 11 occurs every time interval ti1 during a time period covering time stamps t0-6 and occurs every time interval ti2 during a time period covering time stamps time stamps t7-12.
A graph illustrating a discontinuous prediction as known in the art of each position of motor shaft 10 and rotor 11 over the 360 degree rotation of motor shaft 10 and rotor 11 with motor shaft 10 and rotor 11 experiencing an increase in rotational speed between time stamp t6 and time stamp t7 is shown in FIG. 4B. Referring additionally to FIG. 4B, the discontinuous prediction of each position is based on a constant slope equal to 30 degrees divided by time interval ti1 during a time period covering from time stamp to t0 the moment of the speed increase and a constant slope equal to 30 degrees divided by time interval ti2 during a time period covering from the moment of the speed increase to time stamp t12.
A discontinuous prediction as shown in FIG. 4B triggers a potentially harmful torque ripple throughout motor shaft 10 when motor shaft 10 is experiencing any magnitude of acceleration or deceleration. The torque ripple also reduces the economic operation of motor shaft 10. Thus, prior to the present invention, there is a need for a method and device of providing a continuous prediction of the position of motor shaft 10 during an acceleration or deceleration of motor shaft 10.
The present invention relates to a method and device for predicting motor shaft positions that overcomes the aforementioned disadvantages of the prior art. Various aspects of the invention are novel, non-obvious, and provide various advantages. While the actual nature of the present invention covered herein can only be determined with reference to the claims appended hereto, certain features, which are characteristic of the embodiments disclosed herein, are described briefly as follows.
One form of the present invention is a method for predicting a plurality of rotational positions of a rotating shaft upon a first detection of a change in a rotational speed of the shaft from a first speed to a second speed. First, a first rotational position of the rotating shaft as a function of the first speed in response to the first detection of the change in rotational speed of the rotating shaft is predicted. Second, a first incremental rotational position of the rotating shaft that succeeds the first rotational position as predicted is determined. Third, a time interval between the first rotational position as predicted and the incremental rotational position as determined is estimated. Fourth, a prediction slope is estimated as a function of the time interval as estimated, and a differential between the first rotational position as predicted and the incremental rotational position as determined. Finally, a continuous prediction of the plurality of rotational positions of the shaft rotating at the second speed is generated as a function of the prediction slope as estimated.
A second form of the present invention is a system comprising a shaft, two or more sensors, and a controller. The shaft is operable to be rotated over a range of rotation including a plurality of incremental rotational positions. The sensors are operable to provide signals in digital form as an indication of a detection of each rotation of the shaft to one of the incremental rotational positions. The controller is operable to generate a continuous prediction of each rotational position of the shaft over the range of rotation in response to each detection of each rotation of the motor shaft to one of the incremental rotational positions.